Well the simple truth here is that software is very old and never written for PHP 5.3. It integrates with a forum product which was end of life 4 years ago. vBulletin has released a couple security fixes but thats it.
The issue is a simple one you would need to search those files for lines like this
Content visible to verified customers only.
Basically PHP 5.3 does not like =& you would simply change that reference to just = and that should get rid of your error.